Are vertical social networks the future of social media?

I wouldn't call Discord or Goodreads niche. I do think many people are trying to make closely-knit communities because the web feels very impersonal now, with all the marketing and the "influencers" on every platform. The age of being a regular on a large forum has also passed, because most OGs have grown up and probably no longer frequent their old haunts.

I think the future is being able to host your own small, private network and share it with your friends, that you've verified via other means. That means things like Mastodon, small discourse servers, etc are likely what will be used in the future. I don't see phone-based apps changing any time soon, though, and they will be mostly used for formal / quick comms.